This proposal seeks support for a unique investigation of mental health service utilization. The investigation would focus primarily on the National Comorbidity Survey (NCS, Kessler, 1991), the first nationally representative survey of the U.S. household population to administer a structured psychiatric interview. It would also carry out comparative analyses with the Ontario Health Supplement (OHS) , a large household survey in Ontario, Canada. Together, these two surveys contain structured psychiatric interviews and information about service utilization from over 22,000 general population respondents (close to 12,000 in the NCS and over 10,000 in the OHS). The NCS is currently in the field and will be ready for analysis by the time this proposal is funded. The OHS completed field work in April, 1991. The interview schedules used in the NCS and OHS were developed in close collaboration between the U.S. and Canadian investigators. They include identical diagnostic sections based on the WHO Composite International Diagnostic Interview (CIDI, Robins et al. , 1988) as well as identical questions on service utilization and similar questions on the determinants of utilization. The overall goals of the project are to use the diagnostic and services data in these surveys to describe when and where people receive services for psychiatric disorders and how the quantity and nature of services depend on characteristics of the individual and of the organization and financing of services available to the individual. The information on characteristics of the individual is more detailed than in prior investigations and would allow us both to replicate and to extend previous research in a number of ways. The design of the investigation would allow the effects of organization and financing to be studied at three levels of aggregation: at the individual level, by comparing respondents in the NCS who differ in access to and in types of insurance coverage; at the county level, by merging aggregate information on general medical and mental health care resource with the NCS to study geographic variation in access to professional care; and at the cross-national level, by merging data from the NCS and OHS to study variation in patterns and determinants of service use in the U.S. and Canada.